How Do I Get Total Employee By Tosector_Id

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C#

SQL

here is my code of asp

<label class="col-sm-2 control-label">
                   Select Sector:
               </label>
               <div class="col-sm-3">
                  <asp:DropDownList CssClass="form-control" runat="server" MaxLength="7" ID="ddlToSector" OnSelectedIndexChanged="ddlToSector_SelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>
                    </div>
           <label class="col-sm-2 control-label">
               Strenght:
           </label>
           <div class="col-sm-1">
               <asp:TextBox runat="server" ID="txtStrenght" AutoPostBack="true" ></asp:TextBox>
           </div>
       </div>

code behind

var employeeCounts = _service.GetAllEmployeeDuty().Where(x => x.ToSector_Id == '2');
            txtStrenght.Text = employeeCounts.ToString();

I want that when a sector is selected then it total strenght is display in this field,as against each employee there is a sector id is store in the duty table.
in short from employeeduty table column name ToSector_Id collect all the employee for this sector Id and return total no in int